Proper bicycle fit is essential for comfort, safety, injury

Transcription

1 PRACTICAL MANAGEMENT Road Bicycle Fit Marc R. Silberman, MD,* David Webner, MD, Steven Collina, MD, and Brian J. Shiple, DO (Clin J Sport Med 2005;15: ) Proper bicycle fit is essential for comfort, safety, injury prevention, and peak performance. The goal is to balance all of the issues at hand, optimize power and aerobic efficiency, and avoid injury. At an average of 80 revolutions per minute, a cyclist may complete over 5400 revolutions during an hour ride, up to 30,000 revolutions over a 100-mile course, and 81,000 revolutions in the span of 1 week. Compounded over a season, one can see how overuse injuries develop. If properly fitted, the majority of cyclists training correctly will remain injury-free. Bicycle fit consists of static (measurements at rest) or dynamic (measurements while riding) evaluation. Dynamic fit also involves video analysis with concomitant heart rate, wattage, and pedal torque readings. There are 3 contact areas a rider makes with the bicycle, addressed in the following order (Fig. 1): 1. Shoe-cleat-pedal interface 2. Pelvis-saddle interface 3. Hands-handlebar interface Whether a weekend warrior or elite Olympic hopeful, all cyclists are positioned the same, with the exception of the hands-handlebar interface. A recreational rider may prefer to be positioned more upright. STATIC FIT Shoe-Cleat-Pedal Interface For maximal power and injury prevention, the cleat should be positioned so the first metatarsal head lies directly over the pedal axle (Table 1; Figs. 1, 2). For leg length discrepancy, the shoe-pedal interface can be adjusted in 1 of 3 ways. Shims can be inserted between the cleat and the shoe on the shorter leg, custom orthotics may be tried, or the cleat may be moved back slightly on the longer leg. A true discrepancy of greater than 6 mm is considered significant in the cyclist, with some athletes unable to tolerate a difference of 3 mm. 1 One third to half of the difference Received for publication January 2005; accepted May From the *New Jersey Sports Medicine and Performance Center LLC, Gillette, NJ; Sports Medicine, Department of Family Medicine and Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA; and Crozer-Keystone s Healthplex Sports Medicine Institute, Springfield, PA. Reprints: Marc R. Silberman, MD, Director, New Jersey Sports Medicine and Performance Center LLC, 689 Valley Road, Suite 104, Gillette, NJ ( drbicycle@njsportsmed.com). Copyright Ó 2005 by Lippincott Williams & Wilkins should be corrected. If a rider has excessive malalignment of the lower extremity, canted shims or wedges can be used. Heel lifts and most orthotics are not sufficient for cycling as the driving force is through the metatarsal heads. 2 Saddle Height Historical studies on formulas to determine saddle height have been discussed previously by De Vey Mestdagh. 3 These formulas are designed to fit a rider in the highest seated position to produce the most power at a minimal aerobic cost without placing undue stress on the lower extremity. The basic position is that of an almost fully extended leg when at the bottom of the pedal stroke. A formula endorsed by 3-time Tour de France champion Greg LeMond and his coach, Cyrille Guimard, takes the rider s inseam length in centimeters and multiplies it by to equal the saddle height, measured from the center of the bottom bracket to the top of the saddle 4 (Fig. 3). An alternative method is to use knee angle measurements. The knee should be flexed 25 to 30 from full extension, with the pedal in the 6-o clock position 5,6 (Fig. 4). Cyclists who tend to pedal on their toes can tolerate a higher saddle height, whereas those who pedal by driving through and dropping their heels will prefer a lower position. Achilles tendinopathy can result from excessive stretch if the position is too high or from excessive force in the downstroke if the saddle is too low. 1 Saddle Fore-Aft Position When the pedal is positioned at 3 o clock (forward and parallel to the ground), a plumb line dropped from the inferior pole of the patella should hang directly over the pedal axle (Fig. 5). Sprinters and time-trialists will adjust their saddle so the plumb line falls slightly in front of the axle to get on top of the gear in a more forward position. Moving the saddle forward lowers saddle height, whereas moving it backward elevates the saddle. To compete in a time trial with clip-on aero-bars, a rider with one bike may move the saddle slightly forward and higher from the usual road racing position. Saddle Tilt Saddle tilt should be close to level or parallel to the ground. About 60% of body weight can be centered on the narrow saddle. Saddle sores (skin wounds secondary to bacteria, moisture, pressure, and friction), perineal pain and numbness, or impotence may result if the saddle is not wide enough to support the ischial tuberosities or set to a correct height and angle. Time-trialists, who ride on aero-bars in a more forward Clin J Sport Med Volume 15, Number 4, July

2 Silberman et al Clin J Sport Med Volume 15, Number 4, July 2005 TABLE 1. Static Fit: Order of Adjustments and Recommended Neutral Position 1. Foot-shoe-cleat-pedal interface First metatarsal head lies over pedal spindle 2. Saddle height A. Knee angle flexed 25 to 30 short of full extension when the pedal is at the bottom of the downstroke B. Saddle height, measured from center of bottom bracket to the top of saddle, equal to the rider s inseam length in centimeters multiplied by C. Leg extended fully and comfortably (without any pelvis rocking) with heel resting on back of pedal at the bottom of the downstroke (6-o clock position) 3. Saddle fore-aft Plumb bob dropped from the inferior pole of the patella should fall directly over the pedal spindle, with the cranks positioned forward and parallel to the ground (9-o clock position) Note: Recheck saddle height after making fore-aft adjustment 4. Saddle tilt Level to the ground 5. Stem height 0 to 3 inches below the height of the saddle With the hands on the brake hoods and the arms slightly flexed, the torso should flex to 45 in relation to the top tube With the hands in the drops, the torso and top tube angle should be about Stem length or extension With a rider comfortably in the drops with the elbows flexed about 20 degrees, and the knees at their maximal height and forward position, the distance between the elbows and knees should be a small distance, up to 2 inches (make sure rider can stand and climb without hitting knees against bars) With the hands in the drops, looking down, the front hub should be obscured by the transverse part of the handlebars flexed position, prefer a slight downward tilt to decrease saddle pressure on the perineum. Stem and Handlebar Height Stem height is more of a subjective measurement, but is extremely important in terms of aerodynamics, power production, comfort, and injury prevention. With the hands on the brake hoods and the arms slightly flexed, the torso should flex to about 45 in relation to a nonsloping top tube 7 (Fig. 5). When the hands are in the drops, the torso should flex 60 (Fig. 1). The vertical distance between the top of the saddle and the top of the stem or bars should be 1 to 3 inches (5 8 cm) below the saddle, depending on the athlete s flexibility 4,8 (Fig. 3). A recreational rider may prefer to sit more upright, with a shorter reach and higher placed handlebars, for a more comfortable position at the expense of aerodynamics. The rider accounts for 65% to 80% of the total aerodynamic drag. 9 The lower the stem, the more aerodynamic a rider can be, though at the expense of comfort and power. An average size male cyclist can decrease his frontal area by about 30% by moving from the upright touring position to a racing position in the drops. If forward-flexed excessively, maximal sustainable power is often reduced due to diminished crank torque through the top of the pedal cycle. 9 Miguel Indurain (5-time Tour de France champion) and Lance Armstrong (6-time champion) are two notable cyclists with an upright time-trial position despite the total aerodynamic resistance. Handlebar tilt is a personal preference, but most cyclists prefer the lower curve and brake hoods to be slightly elevated. Too often, the bars are tilted downward or the hoods are rotated low, forcing the athlete to overreach. This may result in overuse strain, increased pressure on the hands, and loss of power through the core. 1 FIGURE 1. Order of the three contact areas to address in a bike fit. Torso flexes 60 degrees with hands in the drops. Photo by Mike Spilker. Stem Length or Extension Equally important in the fit of a cyclist is that of upper body position or extension. The athlete s core musculature is extremely vital to performance. Too short a top tube plus stem length (Fig. 4) and the rider will be too bunched up. Too long, and the rider will be too stretched out. When the rider looks down with the arms slightly bent and the hands in the drops, the front hub should be obscured by the transverse part of the handlebars. Also, when the rider is comfortably in the drops with the elbows flexed 60 to 70 and the knees are at their maximal height and forward position, the distance between the elbows and knees should be small, 1 to 2 inches (2 5 cm). The adjustment of upper body extension is achieved through changing the stem length. If the frame was properly fitted, the top tube length will allow an optimum position to be achieved with the use of a 10 to 12 cm stem. 272 q 2005 Lippincott Williams & Wilkins

3 Clin J Sport Med Volume 15, Number 4, July 2005 Road Bicycle Fit FIGURE 2. Cleat is positioned so first metatarsal head lies directly over pedal spindle. DYNAMIC FIT A cyclist s performance capacity is determined by three components: the athlete s metabolism, biomechanics, and aerodynamics. A dynamic evaluation assesses all three of these parameters. Whereas the office examination of the athlete and bicycle is well suited for measuring geometric values, no laboratory investigation can simulate the real-world performance, balance, and aerodynamic issues that confront the athlete out on the road. Video analysis, measurement of wattage, heart rate, and pedal torque comprise a dynamic bike fit. 10 Any adjustments to position can then be re-evaluated in terms of objective rider physiological measurements. If a stem is lowered to provide a more aerodynamic position, but the rider is now too flexed to produce power effectively (demonstrated by lower wattage, higher heart rate, and/or ineffective pedal torque numbers or pattern), then the position change was ineffective. Pedal Torque and Spin Analysis Muscles involved in the power phase drive the crank downward in an effort to rotate the crank, whereas the muscles that are active in the recovery phase are firing primarily to reduce resistance versus the contralateral propulsive limb. Although most athletes believe they pull up on the pedals while cycling, this is rare in road cycling during steady-state efforts and is not essential to an efficient seated pedal stroke. 9 Studies on elite cyclists during steady-state cycling have shown that even on the upstroke, the vector of forces is downward in the opposite direction of the pedal motion. 11,12 The leg in the recovery phase is not lifted as fast as the crank is rotating. The elite cyclist, however, exhibits reduced negative force during the upstroke, in addition to decreased time in producing these forces. 13 There are commercially available tools to evaluate pedal torque. Spin Scan (Racermate) provides net torque, a multicolor graphic depiction of one 360 pedal revolution broken down into 15 segments based on the rider s pedaling technique. An efficient or optimal pedal stroke pattern is felt to be one with a flatter or more even bar graph. 10 An examination of national team riders demonstrated that maximal torque during the downstroke is what differentiated elite athletes from the recreational rider. 13 FIGURE 3. Lemond-Guimard method of determining saddle height. Saddle height = inseam length in cm. Inseam measured by placing a book between legs to simulate saddle and measuring line to mark on wall. q 2005 Lippincott Williams & Wilkins 273

4 Silberman et al Clin J Sport Med Volume 15, Number 4, July 2005 FIGURE 4. Saddle height set so knee angle is degrees with pedal in 6 o clock or dead bottom center position. Bert Webster performing bike fit. Photo by Mike Spilker. In terms of bike fit, pedal torque appears most useful when evaluating injured cyclists and implementing drastic position changes for those riding with aero-bars. Further research needs to be conducted before a pedal torque examination can be universally recommended. INJURIES AND AILMENTS De Vey Mestdagh 3 has described cycling posture based on posture height and posture length. Complaints related to the lower extremity may be addressed by adjusting the saddle (posture height), whereas complaints related to the upper extremities, neck, and back may be addressed by adjusting the handlebars (posture length). The genital, pelvic, and lumbosacral region all fall in an intermediate area. Knee injuries are the most common, and by localizing where the knee hurts, sometimes all that is needed for correction is a small bicycle adjustment (Tables 2, 3). Posterior neck pain and scapular discomfort may be caused by an elongated reach and can be remedied by placing a rider in a more upright position. Ulnar neuropathy or cyclist s palsy, a common ailment, results from excessive pressure on the handlebars. Contributing factors may be bars positioned too low or a saddle too far forward or tilted downward. Hand symptoms may be rectified by increasing handlebar padding, changing hand position frequently, adjusting handlebar tilt and/or height, and rechecking the saddle height. Low back pain may occur in riders who are overstretched on the bike. Riding more upright, raising stem height, and shortening stem length may resolve back discomfort (Table 2). A saddle too high may lead to lower leg symptoms, tibialis anterior, or Achilles tendinopathy. A saddle too low, with excessive heel drop at the bottom of the pedal stroke, may also cause Achilles pain. Correcting saddle height may address these problems. Morton s neuroma or foot neuropathy is common in cyclists and may be due to cleat position, shoe tightness, or shoe-sole irregularities (worn sole with cleat bolts pushing through; Table 2). Knee pain is the most common ailment of cyclists and may be due to training error, poor bike fit, or both. Anterior knee discomfort may be due to a saddle position too low or too far forward in addition to excessive climbing, use of big gears, or too long a crank arm. Adjusting saddle position and modifying training can improve conditions such as patellar tendinosis and patellofemoral pain. Posterior knee pain may occur if the saddle is too high or too far back. Saddle adjustment as well as limiting pedal float can eliminate the discomfort. Medial knee pain can develop from outward pointing toes and/or excessive float in the pedals and can be addressed FIGURE 5. Saddle fore-aft. When pedal is in the 3 o clock position, plumb line dropped from inferior pole of patella falls directly over pedal spindle. Bert Webster performing bike fit. Photos by Mike Spilker. 274 q 2005 Lippincott Williams & Wilkins

5 Clin J Sport Med Volume 15, Number 4, July 2005 Road Bicycle Fit TABLE 2. Overuse Injuries, Contributing Bicycle Posture, and Bicycle Adjustments Ailment Contributing Position Bicycle Adjustment Posterior neck pain, scapular pain for clarity Hand neuropathy (cyclist s palsy, ulnar nerve) Too great of a reach, handlebars too low, too stretched out Too much pressure on bars, handle bars too low, saddle too far forward, excessive downward saddle tilt 1. Ride more upright, shorten reach 2. Raise stem height 3. Shorten stem length 4. Ride with hands on hoods or tops of bars 1. Increase padding on bars and gloves 2. Avoid prolonged pressure, change hand position often 3. Raise stem height 4. Move saddle back if too far forward 5. If saddle is tilted down, position it level Low back pain Too stretched out 1. Ride more upright, shorten reach 2. Raise stem height 3. Shorten stem length Tibialis anterior tendonopathy Saddle height too high Lower saddle height Achilles tendonopathy Saddle height too high (excessive stretch) Lower saddle height Saddle height too low (with concomitant Raise saddle height dropping of heel to generate more power) Morton s neuroma/foot pain/numbness Cleat position Usually, move cleat back, but may be forward Irregular sole Check sole for inner wear or cleat bolts pressing inward Shoes too tight Wider shoes, loosen Velcro straps/shoe buckle Perineal numbness Saddle too high Lower saddle height Tilt angle excessively up or down Adjust angle closer to level with the ground by changing cleat position and limiting float. Lateral knee pain and iliotibial band symptoms may be seen with toes pointing in and/or excessive float in the pedals. Appropriate cleat and pedal modifications can eliminate lateral pain (Table 3). TABLE 3. Bicycle Adjustment Based on the Location of Knee Pain Location Causes Bicycle Adjustment Anterior Seat too low Raise seat Seat too far forward Move seat back Climbing too much Reduce climbing Big gears, low rpm Spin more Cranks too long Shorten cranks Medial Cleats: toes point out Modify cleat position: toe in Consider floating pedals Floating pedals Limit float to 5 Exiting clipless pedals Lower tension Feet too far apart Modify cleat position: move closer Shorten bottom bracket axle Use cranks with less offset Lateral Cleats: toes point in Modify cleat: toe out Consider floating pedals Floating pedals Limit float to 5 Feet too close Modify cleat position: apart Longer bottom bracket axle Use cranks with more offset Shim pedal on crank 2 mm Posterior Saddle too high Lower saddle Saddle too far back Move saddle forward Floating pedals Limit float to 5 Reprinted with permission. 14 Perineal neuropathy is seen with saddles set too high, tilted excessively downward or upward, or too narrow to support the ischial tuberosities. Saddle height and tilt may be reduced (Table 2). The sooner the overuse ailment is addressed through evaluation and modification of training and bike fit, the greater chance of rapid recovery. CONCLUSIONS Proper bike fit is essential for peak performance, comfort, safety, and injury prevention. There is no one set of guidelines or geometric measurements scientifically validated to fit an athlete properly. Each athlete must be fitted individually. Changes should be made during the off-season, one change at a time, in small increments. The goal is to balance all of the issues at hand: injury prevention, aerodynamics, comfort, and performance. The use of video analysis in conjunction with objective physiological measurements such as heart rate, power output and pedal torque has added science to the art of bicycle fit. Whether caring for an elite cyclist or the weekend warrior, the knowledge and skill to fit a cyclist are useful training tools. REFERENCES 1. Baker A. Medical problems in road cycling. In Gregor RJ, Conconi F, eds. Road Cycling. Oxford, United Kingdom: Blackwell Sciences Ltd; 2000: Sanderson DJ. The biomechanics of cycling shoes. Cycling Sci. 1990; September: De Vey Mestdagh K. Personal perspective: in search of an optimum cycling posture. Appl Ergon. 1998;29: LeMond G, Gordis K. Greg LeMond s Complete Book of Bicycling. New York: Perigee Books; Burke ER. Serious Cycling. 2nd ed. Champaign, IL: Human Kinetics; Holmes J, Pruitt A, Whalen A. Lower extremity overuse in bicycling. In Mellion MB, Burke ER, eds. Clinics in Sports Medicine. Vol. 13(1). Bicycle q 2005 Lippincott Williams & Wilkins 275

6 Silberman et al Clin J Sport Med Volume 15, Number 4, July 2005 injuries: prevention and management. Philadelphia, PA: Saunders; 1994: Hughes J. Dr. Andy Pruitt on Bike Fit. Available at: ultracycling.com/equipment/bikefit.html. Reprinted from Ultra Cycling, About Ultracycling Magazine. 8. Armstrong L, Carmichael C. The Lance Armstrong Performance Program. Emmaus: Rodale Press; 2000: Gregor RJ, Conconi F, Broker JP. Biomechanics of road cycling. In Gregor RJ, Conconi F, eds. Road Cycling. Oxford, United Kingdom: Blackwell Sciences Ltd; 2000: Drake S. Dynamic Bike Fit With the CompuTrainer s Spin Scan Takes the Guesswork out of Positioning. Available at: com/html/coaching_corner/dynbikefit-example.htm. 11. Faria IE, Cavanagh PR. The Physiology and Biomechanics of Cycling. New York: Wiley; Broker JP, Gregor RJ. Cycling biomechanics. In Burke ER, ed. High Tech Cycling. Champaign, IL: Human Kinetics; 1996: Broker JP. Cycling biomechanics: road and mountain. In Burke ER, ed. High Tech Cycling. Champaign, IL: Human Kinetics; Baker A. Bicycling Medicine. New York : Fireside, Simon and Schuster, q 2005 Lippincott Williams & Wilkins